Superheating induction furnace



Jan. 5, 1937. J. R. wYATT SUPERHETING INDUCTION FURNACE 2 Sheets-Swat 2Filed March 2 9, 1934 Patented Jan. 5, 1937 UNITED STATES PATENT OFFICEElectric Furnace Corporation,

Philadelphia,

Pa., a corporation of Pennsylvania Application March 29, 1934, SerialNo. 717,994

13 Claims.

My invention relates to the superheating of molten metal preferablyduring pouring, either into a mold or into a ladle from which it is tobe poured into a mold.

The main purpose of my invention is to pour the molten metal from ablast furnace, a cupola, or other container in which it has been melted,through passages subjected to high electromagnetic ilux, either directlyinto the mold or "adle, or with so little storage between as to merelyassist in unifying the flow. This permits melting within a blast furnaceor a cupola by fuel combustion in which the expense of melting is theleast, but where the expense of superheating is high, andelectromagnetically superheating the metal from a temperature below thatdesirable for nal pouring to its nal pouring temperature or above,holding it after superheating where temperatures above nal castingtemperatures are attained.

A further purpose is to electromagnetically superheat molten metal whileit is flowing from the place at which it has been little more thanmelted to the ladle or mold from which, or in which, it is to be cast.

A further purpose is to pass molten metal in parallel through curvedlines of ow about the two sides of a transformer leg and preferablyabout a primary transformer winding to hug the transformer coil closelyand at the same time be heated through secondary action while the metalis flowing through the passages.

A further purpose is to divide the ow of molten metal passing atrelatively low temperature from a cupola or other initial point of vmelting and lea" it continuously-that is, preferably without appreciablestoppage of its flowabout a transformer primary core, to a point ofintended use, whereby the molten metal need not be raised to pouringtemperature in .the cupola, but can be given the necessary pouringfluidity and heating on its way through the divided channels where it issubject to close regulation both by speed of travel and rate of input tothe transformer primary.

Further purposes will appear in the specification and in the claims.

My invention is directed not only to the methods or processes involved,but to structure showing one or more ways in which the methods orprocesses claimed can be carried out. Because of the conditions presentin cast iron my invention finds its higher usefulness at the presenttime in the treatment of cast iron,

but is not restricted to use upon this metal as it is of benefit alsofor any metal in which exact control of the temperature at pouring isdesirable, or in which superheat for pouring or other purposes is betterapplied outside of the furnace of initial melting than inside it.

It is well to distinguish at this point between superheating and pouringtemperature. There are a number of situations inwhich metal issuperheated and subsequently allowed to cool before pouring, so that thetemperature of superheating may be considerably above the pouringtemperature.

From the metallurgical standpoint the principal advantages ofsuperheating cast iron lie in the saving in time and in cost necessaryto secure the proper condition for pouring and in the improved qualityand greater uniformity of the product. By superheating, the: samequality of iron is secured in less time. Stirring assists in this, but,independently of the stirring, superheating results in better quality ofiron in less time than would be secured without superheating.

Superheating sometimes leaves a very desirable effect which persistsafter the superheated metal has solidified. As examples, a few instancesmay be cited in which superheating, as distinguished from mere pouringtemperature, is of importance.

It has been observed that increase of the extent of superheating(without changing the pouring temperature) produces small graphiteparticles, better distribution of graphite particles, and improvedphysical properties in gray cast iron. Tanimura, Influences of coolingvelocity and melting temperature on the graphitization of cast iron, 6Memoirs, College of Engineering, Kyushu Imperial University, Japan (No.2, 1931); Marbaker, High-test gray cast iron-European developments, 37Transactions of the American Foundrymens Association (1929) 405.

The diiculty in duplicating results in a gray iron foundry has been duelargely to not heating the iron sufciently to bring about completesolution of the carbon and the desired degree of homogeneity.

Superheating cast iron incleases its homogeneity and therefore producesa more uniform product. Bremer, Electric-melted iron for cylindercastings, 39 Transactions of the American Foundrymens Association (1931)585, 593, 594.

The extent of formation of iron carbide in iron increases and thendecreases with the temperature of superheating to which the metal issubjected, the critical point being about 2730" F. for 0.06 per centsilicon. The material is likely to be carbidic if cooled from below thistemperature and graphitic if cooled from above this temperature.Increase in silicon lowers the transition point; Marbaker, High-testgray cast iron-European developments, 3'? Transactions of the AmericanFoundrymens Association (1929) 409, 410.

After superheating above the critical point, graphite separates in thecooling iron from an infinite number of tiny nuclei and the resultantgraphite crystals are smaller, more numerous and more uniformlydistributed than would be true for a lower superheating temperature.Superheating assists in obtaining uniformity in hardness as it causesthe graphite to divide more finely and also distributes it moreuniformly. The control of carbon and silicon contents is easier wheresuperheating is used.

Increase of the superheating temperature shortens the malleableizingtime, favors the formation of smaller graphite particles and irnprovesthe physical properties of white cast iron. White and Schneidewind,Effect of superheat on annealing of malleable iron, paper deliveredbefore American Foundrymens Association, at Chicago, June 21, 1933.

My invention is intended to facilitate superl heating and the control ofthe extent of super heating and to provide a maximum of flexibilitycoincidental with a maximum of temperature for the iron. I provide alsofor complete superheating during the flow of the molten metal throughthe electromagnetic superheater which may be an element of an electricfurnace.

In the drawings I have preferred to illustrate a few forms only amongthe many in which my invention may appear, selecting forms which arepractical, efilcient and quite reliable, but which have been chosenchiefly for their suitability in explaining the invention.

Figure 1 is a fragmentary side elevation of my invention.

Figure 1a is a fragmentary side elevation partly in section showing amodification of the structure of Figure 1.

Figure 2 is an enlarged top plan view of a part of Figure 1.

Figures 2a and 2b are fragmentary top plan views showing modificationsof the structure of Figure 2.

Figure 3 is a section of Figure2 parallel to the plane of the paper,corresponding to` a section upon the line 3--3 of Figure 4.

Figure 4 is a section upon the line 4-4 of Figure 3.

Figure 5 is a section taken upon the line 5-5 of Figure 4.

Figure 5a is a fragmentary section showing a modification ofthestructure of Figure 5. Y

Figure 6 is a form corresponding generally with Figure 4, but modied toshow a different transformer. l

Figure 7 is a top plan view of a form corresponding generally with thoseseen in Figures 1 to 5 and in Figure 6, respectively, but havingduplicate paths and multiphase operation.

In the drawings similar numerals indicate like parts.

Taking up nrst the form of Figures 1 to 5, inelusive, I5 indicates anymelting furnace adapted to melt metal in bulk and preferably a blast fni-furnace or a. cupola, or other fuel fired furnace,

from which molten metal is discharged through a launder I6 at atemperature lower than the superheating temperature desired for themolten metal.

In my preferred form this molten metal is run continuously from thefurnace I5 by the launder I6 through a superheater I 'I and into a ladleI8 which pours into a mold I5. During the iiow of the metal it iscontinuously and considerably superheated by electric current developedwithin the molten metal as a secondary by an alternating currentprimary. The current may be of commercial frequency, passed through aprimary Winding 20 Wound upon the interior leg 2l of a suitablylaminated transformer core 22. The winding 20 may desirably be insulatedwith heat resisting enamel. The transformer is shown in Figures l to 5,inclusive, to be of shell type, provided with return legs 23 and 23. Theprimary winding 20 is preferably formed as a single layer of turns uponinsulation 24 which surrounds the interior transformer leg 2|, and theprimary winding may be spaced as at 25 from the inside 26 of therefractory 21 within which the branched channels for the molten metalare formed. The space 25 may carry a blast of air for cooling purposes.

My preferred form of superheating channel surrounds the primary windingas closely as may be, with proper cooling space and a reasonablethickness of refractory wall. The channel 28 connects with the launderkI6 by an inlet opening 29, and discharges through an outlet opening 30,having a spout 3|. The branches 32 and 33 which separate at 34 joinagain at 35.

The preferred flattened character of the inlet and outlet openings' 29and 30 will appear from comparison of the cross-sections seen in Figures3 and 4.

Though the mere flow of the metal from an elevated launder may affordsufficient head to pass the molten metal through the superheatingchannel, it is desirable to use a closed launder so that the hydrostatichead of the metal in the furnace I5 will maintain pressure upon themolten metal flowing through the superheating channel.

The hydrostatic head of the furnace I5 transmitted through the closedlaunder not only assists in giving a quick even flow of molten metalthrough the superheating channel, but performs a very importantadditional function. It is to be noted that the superheating channel isclosed or submerged, so that pressure can be maintained upon it. Withthe high energy input necessary to superheat a rapidly moving stream ofmolten metal, pinch effect will pinch off" or interrupt the stream ofmolten metal and break static head at the furnace (inlet) end of mysuperheater is desirable to make it possible to use a higher rate ofheating in the superheater without trouble, from pinch effect, it isdesirable also to prevent blowing out of the metal at the pouring spoutfrom this cause since the pinch effect operates in both directions.

vpouring spout unnecessary the outlet may be at the same level as thesuperheater and such a construction is shown in Figure 5a. The pouringspout 3I is here horizontal.

In Figures 1 and 5 I have attempted to differentiate between the inlethead and the head at the pouring spout, making the head at the pouringspout lower than that shown within the launder I6 for the pur-pose ofpointing out diagrammatically that at the inlet end a head is requiredto cause movement through the superheater which head is additional tothat required to prevent interruption of the circuit by pinch eiect. Forthis reason the diagrammatic illustration of the pouring spout head isshown as equivalent to a part only of the head given in the launder I6.

Where the metal is to be passed through the superheater continuously, i.e., is continuously to be in motion, the point 35 at which the dividedpaths of the superheater meet may be at some distance from theV outletof the pouring spout, (as in Figure 2) without danger of trouble fromchilling. n

If the molten metal is to be held molten in the superheater, thesecondary current must pass through substantially all of it and apouring spout or launder carrying metal located at any considerabledistance from the superheater divided channels would be likely to givetrouble by chilling. For this reason I have shown in Figures 2a and 2bfragmentary diagrammatic illustrations in which the divided pathsseparate substantially at 35 at the furnace gate and recombine at 34substantially at the outlet of the pouring spout.

By extending the division to cover the entire or nearly the entiredistance from the furnace to the outlet of the pouring spout thesecondary current is passed through substantially the entire path of themolten metal and chilling is prevented.

If current is not to be maintained in the superheater it should becapable of being emptied.

It will be obvious that any mechanism by which the head may bemaintained and the superheater may be tilted will serve the purpose. Inthe instant case the upper end of the launder I6 may constitute a.trough as in Figure la receiving the molten metal from the cupola outletleaving the superheater free for such movement and replacement as may bedesired. In this event the entire head relied upon must be within thelaunder. N

Where the pouring outlet is horizontal the metal will flow out freely.

Where it is the intention to keep the current on during intervalsbetween use of the superheater the launder may be connected xedly withthe furnace to allow use of head within the furnace but in this case-andin any casesome means of stoppage of flow within the launder must beprovided. I have shown this diagrammatically by gate 43.

In order that the power factor of the superheater may be high, thecross-section of the channel must be reasonably small so that theresistance of the secondary circuit will be relatively high.

The path of the branched channel is as close as reasonably possible tothe primary winding 20 and to the interior leg 2I of the transformercore 22, 'in order to obtain close coupling. In

the form of Figures l to 5, inclusive, there is a complete magneticcircuit through the core and between the branches 32 and 33 of thechannel.

In operation, the molten metal, which will ordinarily be melted in thefurnace I5, is cai'- ried by the closed launder I6 into the inletopening 29 of the electromagnetic superheater. The molten metal dividesat the point 3@ and flows in parallel through the branches 32 and 33 tothe point 35 where the branches join. At the point 35 the molten metalenters the outlet l opening 38 and flows from the spout 3| into theladle I8, which pours into the mold I9.

While the continuously flowing molten metal is passing through thechannel branches 32 and 33, secondary current is induced in the metal bythe primary winding 20, which sets up flux in the transformer core 22.The secondary current flows around the circular channel, superheatingthe molten metal in the channel. The superheating progressescontinuously notwithstanding that metal enters the inlet opening 25 andleaves the outlet opening 30 of the channel during the operation of thesuperheater. Thus the superheater acts upon flowing metal or metal intransit to the point of casting.

The ladle I8 is not essential, and in fact I show in Figure 7 pouringdirectly from lthe superheater into the mold I9. The ladle I8 performsseveral desirable functions, however. It receives the superheated moltenmetal while molds are being changed, and, for a time, takes up theadditional flow lin case the rate of flow of the molten metal from themelting furnace is faster than the rate of pouring into the final mold.It also receives the molten metal from the launder .and channel duringinterruption of the operation, after the flow of metal from the furnaceI5 has been cut off in any well known manner, and makes it possible torecharge from the ladle into the furnace I5 the metal drained from thesuperheater and not required to ll the last mold.

The ladle I8 (or a holding furnace to perform its function) also offersa distinct metallurgical advantage in some instances, by cooling themolten metal from the superheating temperature down to the pouringtemperature.

where it is not desirable to pour at the temperature of superheat. Incertain cases, the molten metal is superheated for any suitable purpose,such as one of the purposes referred to above, but the superheatingtemperature is too high for proper pouring. The superheated metal maythen be held in the ladle until it cools to a Satisfactory pouringtemperature, at which time it may be poured.

While I prefer to use a shell type transformer core, as shown in Figuresl to 5 inclusive, a core type transformer core may be used as shown inFigure 6. In this gure a core type transformer core 22 has an interiorleg 2i and a return leg 232. The winding and channel construction arethe same as that employed in the form of Figures 1 to 5, inclusive..

The operation of the form of Figure 6 is the same as the operation ofthe form of Figures 1 complete the secondary circuit.

In Figure 7 a superheating furnace, of the type which may be used forpolyphase operation, is shown. The launder I6 separates at 36 into twobranches 31 and 38, one of which :supplies molten metal toi asuperheater Il', which may be identical with the superheater shown inFigures 1 to 5, inclusive, and connects to one phase of a two phasesource, and the other of whichsupplies molten metal to a similarsuperheater f1, which connects to the other phase of the two phasesource. The `molten metal from the superheaters I1 and I1 entersconduits 39 and 40 which join at 4| near the outlet opening 42.

The operation of the form of Figure 7 ls similar to the operation of theother forms. Molten metal from a blast furnace, cupola or other suitablefurnace, preferably under considerable pressure due to the head ofmolten metal, enters the launder I6', divides at 36 into the branches 3land 38flows continuously through the parallel branches of thesuperheaters I'I and I1', where it is superhcated as it flows along,leaves by the conduits 39 and 40, joining at 4I,a.nd discharges from theoutlet opening 42 into the mold I9.

'I'he electromagnetic superheating obtained in the present invention isparticularly desirable because it produces superheating quickly, as themolten metal flows to the point of casting, and therefore avoids heatlosses and metal losses and the destructive action on the furnace whichIwould be present in case the superheating were attempted in the blastfurnace, the cupola or in some other furnace which might be employed forthe purpose.

While my invention may be best suited to superheating cast iron it isalso applicable to steel, as for example to secure uniformity oftemperature among Bessemer converter heats, or to nonferrous metals, forinstance to reduce metal losses while superheating to obtain the properpouring temperature.

'I'he superheater of my invention produces thorough mixing of the metaldue to the agitation accompanying flow through the superheater channel.'I'his is desirable to homogenize the metal.

An important advantage of my invention is the economy with whichsuperheating is obtained, since the initial heating efficiency is veryhigh, as the heat is actually developed in the molten metal itself, andsince the molten metal is available for casting or other use immediatelyafter superheating, so `that it is not necessary to make up for heatlosses while holding the molten metal at the temperature of superheat,

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. The method of superheating molten metal, after it has left a furnacein which the molten metal is contained, which consists in progressingthe metal wholly outside the furnace, while fully molten, subsequent toany smelting and subsequent to any refining action, as a continuouslyflowing unidirectional stream of a cross section having substantialresistance through an inductive heating magnetic field effective for thedesired superheating whilethe molten metal is in motion from the furnacein which the metal was melted to the point of use, thus inducing asecondary current within the stream, and in maintaining a substantialhydrostatic head of molten metal on the stream to avoid interruption ofoperation due to pinch efl'ect.

2. The method of superheating molten metal.

after it has left a furnace in which the molten metal is contained,which consists in progressing the metal wholly outside the furnace,while fully molten, subsequent to any smelting and subsequent to any,refining action, in a stream of cross section having substantialresistance through i an inductive heating magnetic field effective forthe desired superheating while the molten metal is in motion from thefurnace in which the metal was melted to the point of use, inelectrically connecting points on the stream respectively behind andforward of the magnetic field through molten metal, inducing a secondarycurrent within the stream, and in maintaining a substantial hydrostatichead of molten metal throughout the portion of the stream underinduction heating to avoid interruption of operation due to pincheffect.

3. 'I'he method of superheating molten metal after it has left a fuelfurnace while pouring it fully molten from the fuel furnace to a ladleor mold within which or from which it is to be cast, which consists inutilizing the fully molten metal in the fuel furnace to give a head andmaintaining the pressure from the head while dividing the paths of themolten metal wholly outside of the fuel furnace and maintaining the headalso throughout the divided paths, recoxnbining the divided paths forthe pouring, in passing the molten metal hydraulically in parallelthrough the paths from the point of dividing to the point ofre-combining, and, while the paths are divided, electromagneticallyheatingthe molten metal by inducing secondary current throughout thedivided paths from division point to meeting point in series as themetal is flowing, producing superheating of the molten metal by theintensity of the induced current while the molten metal is in flow inthe paths.

4. The method of superheating molten metal after it has left a furnacein which the molten metal is contained, using the secondary effect of anelectric current passing about'a transformer core, which consists inflowing the metal wholly outside the furnace and while fully molten,into close proximity to the core, While maintaining about the core analternating current efl'ective to superheat the molten metal while it isin flow, in dividing the metal into unidirectional streams passing inparallel about the core at substantially the same distance therefrom. inuniting the streams and in pouring the molten metal continuously as itis superheatei.

5. The method of progressively superheating molten metal, after it hasleft a furnace in which the molten metal is contained, which consists inmaintaining a head of molten metal, flowing a submerged stream of moltenmetal wholly outside of the furnace and while fully molten, to and inparallel about the core of an electromagnetic transformer, whilemaintaining about the core an alternating current effective to superheatthe molten metal while it is in flow and uniting the divided parts ofthe stream of molten metal, in maintaining the flow about the coresubstantiallyv the same distance from the core and in pouring the moltenmetal as it is superheated. y

6. The method of making castings of superior quality, which consists inproducing fully molten metal in one furnace under fuel-flred conditions,in tapping off the molten metal from said furnace, in dividing thetapped molten metal wholly outside said furnace into submerged branchingunidirectional streams, in subsequently uniting 3Q pouring, in coolingthe united stream of molten` a plurality of unidirectional streams, inmaintaining a substantial hydrostatic head of molten metal throughoutthe branched streams to avoid interruption of operation due to pincheffect, in inducing alternating current in the molten metal circuitformed by the subsequently uniting branched unidirectional streamscontinuously as the molten metal fiows toward the point of casting andeffective to superheat the molten metal while it is in iiow, in coolingthe united stream of molten metal to a pouring temperature substantiallybelow the superheating temperature and in later casting the unitedstream of kmolten metal which has undergone superheating and cooling.

7. The method of making metal castings of superior `quality, whichconsists in producing fully molten metal in one furnace underfuelredsconditions, in tapping off the molten metal from said furnace,in continuously flowing the molten metal in submerged unidirectionalstreams of cross section having substantial resistance, toward the pointof pouring, in maintaining a substantial hydrostatic head of moltenmetal throughout the branched streams to avoid interruption of operationdue to pinch effect, in inductively superheating the molten metal whollyoutside said furnace while it is flowing to the point of pouring and atthe intended rate of metal to a pouring temperature substantially be,low the superheating temperature and in pouring -the molten metal afterit has undergone superheating and cooling.

8. A fuel melting furnace, a closed launder connected therewith at thepoint of tapping the fully molten metal therefrom, walls forming adivided closed channel which is entirely filled with moltenmetal duringthe operation, conf nected with the launder at the point of division ofthe channel and re-connected to feed into an outlet opening, the metalin the channel form- 'ing a complete/ metallic circuit, and atransformer leg and primary thereabout enclosed by the channel, 4thelevel of molten metal in the fuel-fired furnace being at all timesduring Vthe operation of the launder substantially above the outletopening, whereby the molten metal within the fuel-fired furnace providesa head for the metal in the channel andis superheated inductivelywhollyoutside the fuel-fired furnace.

`9. In a metallurgical apparatus, a furnace adapted to produce moltenmetal, an electric induction superheater wholly outside said furnace andsubstantially free from smelting and from refining action, comisingwallsforming a charging opening, Walls forming a discharge opening, wallsforming a plurality of submerged channels communicating with thecharging opening at the inlet side and communicating with the dischargeopening at the outlet side, the

vchannels being entirely filled with molten metal dur-ing operation, andthe metal in the channels forming a complete metallic circuit, a launderconnecting the tap opening of said furnace with the charging opening ofthe superheater, the level of molten metal in the furnace being abovethe level of the-superheater, a core surrounding one of the submergedchannels and a winding around the core, whereby molten metal 'issuperheated outside of said furnace after it has left said furnace andwhile it is in flow.

10. In a metallurgical apparatus, a fuel-fired furnace adapted toproduce molten metal, an electric induction superheater wholly outsidesaid furnace and substantially free from smelting and from refiningaction, comprising Walls forming a charging opening, walls forming adischarge opening, walls forming a plurality of submerged channelscommunicating with the charg ing opening at the inlet side andcommunicating with the discharge opening at the outlet side, thechannels being entirely filled with molten metal during operation,andthe metal of the channels forming a complete metallic circuit, alaunder connecting the fuel-fired furnace with the charging opening ofthe superheater, the launder being not lower than the bottoms of thesuperheater channels, a core surrounding one of the submerged channelsand a winding around the core, whereby molten metal is super.- heatedoutside of said furnace after it has left said furnace and while it isin flow.

11. In a metallurgical apparatus, a fuel-fired l 'furnace adapted toproduce molten metal, an

electric induction superheater wholly outside said furnace comprisingwalls forming' a charging opening, walls forming a discharge opening,walls forming a plurality of submerged channels communicating with thecharging opening vat the inlet side and communicating with the dischargeopeningat the outlet side, the channels being entirely filled withmolten metal during operation, a closed launder connecting thefuel-fired furnace with the superheater, there being gravity flowthrough the launder and superheater from the fuel-fired furnace and thelevel of molten metal in the fuel-fired furnace being substantiallyhigher than the levei of molten metal in the superheater, a coresurrounding one of the submerged channels, and a coil around the core,whereby a hydrostatic head of molten metal from the fuel-fired furnaceis rmaintained 0n the superheater to prevent interruption of the circuit due tol pinch effect and molten metal is superheated outside ofsaid furnace after it has left said furnace and while it is in iiow.

12. An induction electric furnace comprising a launder forming both apassage and a hydraulic head, a submerged divided channel for which thelaunder forms the head, the channel being entirely filled with moltenmetal during operation, a pouring spout into which the flow from thedivided channel is guided and which also affords hydraulic head to thedivided channel, a transformer having a leg enclosed by the dividedchannel and primary alternating current supply for the transformer leg.

CII

13. An induction electric furnace comprising e a launder forming both apassage and a hydraulic head, a submerged divided channel for which thelaunderforms the head, the channel being entirely'iilled with moltenmetal during operation, a pouring spout into which the flow from thedivided channel is guided and which

